Why did the openai's gym website close?
According to Open AI's Greg Brockman, the Gym website never had a big impact and so was never maintained. This is the reason he gives for shutting down the website. 

A read only export of the site was archived at https://gym.openai.com/read-only.html and if you attempt to access the old website through the url https://gym.openai.com you will be redirected to the Open AI gym github repository. 

For a while a static copy of the Open AI leader-board was maintained on the below url https://scoreboard-site-1764008611.us-west-2.elb.amazonaws.com/ . However as of present the static site is also unreachable. 

The Canadian AI startup montreal.ai had offered to maintain the gym website. However this offer was not taken up by open ai. 

This issue was discussed in depth on the following threads

https://www.reddit.com/r/MachineLearning/comments/6zvlm2/d_openai_closing_down_gym_toolkit_website/?st=jca6ia3n&amp;sh=48a0d8f3

https://github.com/openai/gym/issues/718